Ventilation systems are present in almost every building. Ventilation systems are used to ensure a continuous supply of fresh air to the building. The energy required by the air transfer is dominated by the volume of air to be transferred and the pressure losses generated by the transferred air. Thus, if ventilation systems are to be made more efficient, the pressure losses should be minimized.
The pressure losses are mainly generated by the system filter, the duct bends, the piping and the control valves at each room. It can roughly be said that the filter pressure losses and the control valve pressure losses are much more significant than the duct pressure losses. The ducts are designed so that the pressure loss is less than 1 Pa/m in order to reduce the noise caused by air passing in the ducts. The pressure losses of a control valve are usually in the order of 1 to 100 Pa, and the filter pressure losses are normally in the order of 150 Pa. The control valve pressure losses are adjustable and should thus be minimized to ensure energy efficient operation of the ventilation system.
The tuning of the ventilation system is carried out after the installation of the ventilation system. The tuning phase is extremely important, and careless tuning can easily undo an energy efficient designed and dimensioned ventilation system. The proper ventilation tuning according to known methods is an iterative and time consuming process. In addition, the accurate measurement of pressures and air flow rates is difficult with hand held equipment in field conditions. In known tuning methods, the valve in the furthermost branch is opened and the valves in the other branches are closed. The air flow rate in the furthermost branch is then set to a desired level by adjusting the rotation speed of the fan driven by the frequency converter controlled electric motor to an appropriate level. The rotation speed of the fan is then kept at this level, and the valves in the other branches are adjusted so that a desired air flow rate is achieved into each branch. When each branch has been set, the flow rate of the furthermost branch must be adjusted once again by adjusting the rotation speed of the fan. The rotation speed of the fan is then kept at this level, and the valves in the other branches are once again adjusted so that a desired air flow rate is achieved into each branch. The need of the further iteration rounds is due to the fact that when the flow rate to the other branches are increased, the pressure produced by the fan drops, which means that the flow rate to the branch first tuned also drops.